AAC Plant Process

Raw material preparation is the first step in AAC plant manufacturing process.Fly ash is mixed with water to form fly ash slurry. Slurry thus formed is mixed with other ingredients like lime powder, cement, gypsum and aluminum powder in proportionate quantity to form blocks. Lime powder required for AAC production is acquired by crushing limestone to fine powder at AAC factory or by directly purchasing it in powder form from a various plants.

A dosing and mixing unit is necessary for best homogenous quality. Fly ash is pumped into a container. Once the desired weight is poured in, pumping is stopped. Similarly lime powder, cement and gypsum are poured into individual containers using conveyors. Once required amount of each ingredient is filled into their individual containers control system releases all ingredients into mixing drum. A smaller bowl type structure used for feeding Aluminum powder is also attached as a part of mixing unit. Once the mixture has been churned for set time, it is ready to be poured into molds using dosing unit. Dosing unit releases this mixture as per set quantities into molds.

Casting, rising and curing are vital intermediate steps for perfect AAC admixture. Before casting, molds are coated with a thin layer of oil in order to ensure that green-cake does not stick to molds. While slurry is mixed and poured into greased molds, Aluminum reacts with Calcium Hydroxide and water and releases hydrogen gas. This leads to formation of tiny cells causing slurry mix to expand. Such expansion may be thrice its original volume. Bubble size is about 2- 5mm. When rising process is over, green-cake is allowed to settle and cure. Usually rising and pre-curing process takes around 1-4 hours. Rising is dependent on raw material mix and weather conditions. At end of precuring process, green-cake is hard enough to be wire cut as per requirements. AAC is cured in an autoclave.Steam is fed into the autoclaved at high pressure, typically reaching a pressure of 800kPa to 1200 KPa and a temperature of 180°C.

After achieving cuttingstrength, cake is ready to be demoulded.Once a mold is out of pre-curing room, it is lifted by a crane for demoulding operation. While all previous processes like raw material preparation, dosing & mixing and casting are pretty much same across all technologies, demoulding and cutting process vary vastly depending on technology provider.